Fluorescence Properties Of Dissolved Organic Matter (DOM) Produced By A Mixotrophic Dinoflagellate *Alexandrium Fundyense*
Cawley, Kaelin 1 ; McKnight, Diane 2
1 University of Colorado at Boulder
2 University of Colorado at Boulder
Algae have been shown to release DOM during growth. Further, DOM from algal sources has been shown to have distinct chemical properties when analyzed with spectral techniques. At the same time some algal species, including harmful algal bloom forming species, can be mixotrophs, i.e. they may be able to use DOM as a carbon source. We applied fluorescence spectroscopy to study DOM excretion and uptake by algae in surface waters. To elucidate the fluorescent properties of DOM produced by algae responsible for paralytic shellfish poisoning in the Gulf of Maine we grew Alexandrium fundyense in laboratory culture and fluorescence excitation-emission spectra were collected from samples of the culture medium. DOC concentrations, total dissolved nitrogen, and cell density were also measured. Spectra were modeled using the Cory and McKnight (2005) PARAFAC model. An increasing DOC concentration, UV-vis absorbance, and fluorescence index value with increasing cell density indicate an increase in the amount and algal character of the DOM in the culture solution. Additionally, PARAFAC modeling showed an increase in the fluorescence loadings of several components associated with microbial DOM sources, including quinone-like components and a tryptophan-like component. These results show that fluorescence spectroscopy is an effective technique for tracking the composition of the DOM pool as it changes with algal inputs.